The expansion of communication networks of the Ethernet type is today made both as previously to offices and to a particular great extent to private homes due to the fact that also private subscribers want to have access to broadband communication. For densely located private homes such as apartments in apartment buildings solutions are used which in principle are Ethernet-based local networks of the standard type used for offices. However, the structure of local networks for such apartments differs from that of local networks installed in offices by the fact that apartments in the same building are located at larger distances of each other than the rooms in an office. In addition, often the distribution of electric power is not made in the same careful way, in particular as to the distribution of a common electrical ground. For a network of the Ethernet type that utilizes electrical twisted pair conductors, the maximum distance is 100 meters between a connection node like a switch and a computer connected thereto. Such a limited maximum distance commonly results in that only a few apartments in an apartment building can be connected to the same switch, this resulting in a high installation cost per connected apartment due to the cost of the switch together with the fact that a special room that can be locked and possibly has climate conditioning must be provided. Possibly, electrically shielded cables could be used to avoid not permitted interference but this possibility is often very limited due to the unsatisfactory distribution of electrical ground. Furthermore, an electric cable is always installed for a particular transmission rate (bit rate) and its possibility of being capable of transferring information having a considerably higher rate is therefore limited.
By connecting subscribers in a local network by optical fibers the difficulties and disadvantages mentioned above are avoided. By using optical fibers thus all electromagnetic interference is avoided, communication is easily obtained over large distances and the information transmission can most often be fairly easily upgraded to higher rates by replacing components directly connected to the fibers. However, the cost for converting between optical and electrical signals is high when using conventional components.
The systems that are today offered for introducing optical fibers as part of transmission links in networks include in addition to the very optical fibers primarily relatively large, individual modules for converting between electrical and optical signals, each one of the modules connected to an individual optical fiber or individual optical fiber pair. The modules are collected at the switch in a rack and are by a short unshielded or shielded, electrical multi-conductor cable connected to the switch that is generally placed near the modules in the direct vicinity of the rack. Each module then has both an electrical connector and an optical connector on its “front side”. Furthermore, each such module has a complete, electrical Ethernet interface and could thus also operate together with an electric connection cable, the length of which can comprise up to 100 meters. The modules are furthermore provided with electronic circuits that can verify the integrity of both the electrical connection and the optical connection by illuminating suitable light emitting diodes. Extremely seldom the possibility exists of directly verifying the total link in other ways than by a method related to a protocol of the type comprising the PING command in IP (the “Internet Protocol”) to verify the connection with some IP address.
Switches having optical ports for a direct connection to optical fibers are also used but they are most often not less costly than the combination of a common electrical network switch having electrical output terminals and separate converter modules.
In order to change connections in networks it is common that the fixed connection to a peripheral unit/network terminal through a connector is available in a connection board that is coupled to the switch by short connection cables. A corresponding method of connecting that instead of electrical lines uses optical fiber cables can have significant disadvantages, since fiber cables are more easily mechanically damaged than electrical cables and since detachable optical fiber cables having at each end optical connectors mounted thereto are required instead of the short electrical connection cables or in addition to the electrical connection cables in the case where conventional converters for converting between electric and optical signals are used. However, optical connectors are costly and require a rather costly mounting operation, and thus such a switching feature in the network results in costs that are totally too high. An optical cable for use instead of electrical cables in local networks is disclosed in Japanese patent application 10079745. The cable has in each end connectors comprising circuits enclosed therein for converting between electrical and optical signals.